This invention relates to acoustical flowmeter systems and is particularly directed to an improvement in the acoustical flowmeters of the type described and claimed in the U.S. Pat. No. 4,164,865 entitled, "Acoustical Wave Flowmeter" by L. G. Hall and R. S. Loveland, which issued Aug. 21, 1979 and the flowmeter of the U.S. Pat. No. 4,003,252 entitled, "Acoustical Wave Flowmeter" by E. J. DeWath, which issued Jan. 18, 1977.
The transducer of the Hall and Loveland system eliminated all impediments to the flow path of the fluid, all cavities in which debris might collect, measured flow accurately regardless of changes in fluid composition or temperature, and determined a change in velocity of sound of the fluid being measured as a function of fluid density. The advantages of the Hall and Loveland system, and manner in which the system functions, is clearly set forth in the Hall and Loveland patent, supra.
Since this is a very highly accurate fluid flow measuring system, one of the many applications is to determine the velocity of fluid or gases (volume flow rate) inspired and expired by a hospitalized patient suffering from lung disease or recent chest surgery. However, such an environment is hostile to the proper operation of the system because of the temperature at which the room, an intensive care unit (ICU) for example, is maintained. The air delivered to the patient's lung is 100% saturated and the room where the system is located is at a temperature which normally causes water to condense out of the delivered and expired air. As a consequence, an accurate determination of volume flow rate cannot be made if water droplets form on the inside of the transducer, or if water condenses in the connecting tubing and is allowed to run through the transducer.
This invention overcomes the problem of operating in such an environment and enables an accurate determination of the volume flow rate inspired and expired by the hospitalized patient and adapted to be connected to standard air delivery tubing as used in hospital intensive care units.